Aircraft wings typically comprise a series of actuable control surface elements. These control surface elements define control surfaces (also known as auxiliary aerofoils) which are moveable relative to the fixed wing structure in order to alter the aerodynamic characteristics of the wing. Such control surface elements include leading edge devices such as slats, and trailing edge devices such as flaps.
Typically, control surface elements are actuated at either span-wise end by two separate actuators. It is conceivable that if either of these actuators malfunctions, inconsistent actuation and skew or loss of the relevant control surface could occur. It is important that if skew or loss is detected, the relevant systems are shut down and the pilot of the aircraft is notified.
Various methods have been proposed in the prior art for providing detection of skew and/or loss of control surface elements. One such system described in U.S. Pat. No. 5,680,124 proposes a cable which is coupled to each of a series of control surface elements. The cable is put in tension in the event of skew or loss. A movement detector with a proximity sensor is provided coupled to the cable such that any movement of the cable resulting from skew and/or loss can be detected. This detector is mounted on the endmost flap or slat. It is coupled to the flap/slat electronics unit (FSEU) in the aircraft fuselage via electric cables running from the moveable control surface element through the fixed wing structure into the fuselage and to the FSEU.
This system detects skew by differential motion of adjacent surface elements which acts to pull the cable. A first problem with this system is that because the cable must be anchored at the endmost control surface elements, skew of those elements cannot be easily detected by this system. For example, if the endmost surface drive mechanism fails to move, this will not necessarily result in differential motion between the endmost surface and the next surface.
A further problem with this prior art system is that wiring needs to be routed between the moveable control surface element on which the detector is mounted to and the fixed wing structure. Translating wiring between a moveable structure and a fixed structure is undesirable as wear and fatigue can occur. Furthermore, such wiring will be exposed to, and subject to, damage by external elements.
In addition, leading edge control surface elements such as slats need to have anti-icing features. Such features generate a range of adverse temperature conditions which can affect the performance and reliability of the cable pull detector mounted on these control surface elements.
A further problem with the prior art system is that the moveable control surface element is usually an enclosed panel, making access to the sensor difficult for maintenance.
A still further problem with the prior art system is that a broken cable can not be detected. If the cable is broken then the skew or loss can no longer be detected which compromises the safety of the system. A check is therefore required at regular intervals to verify the cable is intact. This is a manual operation which adds maintenance time, cost and administration effort.